Agricultural combines are large machines that harvest, thresh, separate and clean an agricultural crop. The resulting clean grain is stored in a grain tank located on the combine. The clean grain can then be transported from the grain tank to a truck, grain cart or other receiving bin by an unloading auger.
A grain harvesting combine has a header which cuts the crop and feeds it upward into a threshing and separating rotor within a housing having a perforated wall. The rotor rotates within the housing, passing grain within clearances between the rotor and perforated housing to thresh grain from the crop.
Rotary combines have one or two large rotors for threshing and separating the harvested crop material. In most rotary combines the rotor or rotors are arranged along the longitudinal axis of the machine. These rotors are provided with an infeed section for receiving harvested crop material, a threshing section for threshing the harvested crop material received from the infeed section and a separating section for freeing grain trapped in the threshed crop material received from the threshing section. Examples are shown in U.S. Pat. Nos. 5,445,563; 5,688,170 and 7,070,498, herein incorporated by reference.
The threshed grain falls onto a grain pan, and from the grain pan onto a set of upper and lower sieves. The sieves are oscillated, causing clean grain to fall through for collection. A blower blows air upward through the sieves, discharging chaff to the rear. Straw from the threshing chamber proceeds through a straw beater and out the rear of the combine.
The clean grain is collected and conveyed to the grain tank. Incompletely threshed grain will not proceed through the fingers of the sieves, yet is too heavy to be blown out the rear along with the chaff. This grain, called “tailings” or “returns” is often returned to the threshing and separating rotor for rethreshing. However, when tailings are returned to the rotor for rethreshing, under some grain conditions, called “white caps”, tailings will pass through the rotor yet again without the grain separating from the chaff.
Some prior art grain harvesting combines have dedicated rethreshing rotors for receiving tailings from the sieves, rethreshing the tailings, and passing the tailings back through the primary rotor for rethreshing.
U.S. Pat. No. 5,498,206 discloses a grain combine that includes a primary threshing rotor which rotates to thresh grain from crop, a sieve section for separating grain from chaff, a clean grain conveyor, a clean grain storage tank, and a rethreshing section for rethreshing tailings. The rethreshing section has a rethreshing rotor which receives the tailings from the sieve section. The rethreshing rotor extends completely across an end of the sieve section for rotating about an axis which extends in parallel to the end of the sieve section. The rethreshing rotor includes rasp bars which extend along the end of the sieve section for receiving the tailings and pressing the tailings against a rethreshing pan. Blowers are provided for removing loose chaff from the tailings in the rethreshing section. The rethreshed tailings, including clean grain separated from the tailings by rethreshing, are returned to the primary rotor for rethreshing.
The present inventors have recognized that some prior methods are limited in their ability to prevent grain damage in damage-sensitive crops. The present inventors have recognized that returning tailings directly to the primary threshing and separating rotor leads to greater losses, due to grain re-introduction into the primary rotor, i.e., grain can be recirculated in an endless loop.